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    <script>
        function downCount( end){
            var start = new Date()

            var ms = +end - +start 
            var s = ms / 1000
            var dd = parseInt(s / 60 / 60 / 24 )
            var hh = Math.floor(s / 60 / 60 % 24 )
            var mm = Math.floor( s / 60 % 60 )
            var ss = Math.floor( s % 60)

           return  {
               tian : dd,
               shi : hh,
               fen : mm,
               miao : ss
           }
        }
         
         var res = downCount(new Date('2020/08/26  16: 50: 00') )
         document.write( '距离下课 还有 ' + res.tian + '天' + res. shi + '时'+ res.fen + '分'+ res.miao + '秒')
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